Global phylogeography and population genomics of the commercially exploited smoothhound shark, Mustelus mustelus.

Winn, J.*¹, Bester van der Merwe, A.¹, Maduna, S.²

¹ Stellenbosch University, Genetics Department, Western Cape, South Africa
² Department of Ecosystems in the Barents Region, Svanhovd Research Station, Norwegian Institute of Bioeconomy Research, Svanvik, Norway

Accelerated global warming and over-exploitation of marine species threaten to eradicate the unique genetic archives of modern Chondrichthyans (sharks, rays, and chimeras), an evolutionarily robust lineage with a 400-million-year genealogy. Understanding the impact of rapidly changing global conditions on elasmobranchs (sharks and rays) and devising conservation responses relies on the identification of unique genetic populations adapted to specific environmental niches. The genetic mechanisms underlying climate-related adaptation in elasmobranchs are poorly understood, however it is now widely accepted that the mitogenome is under selection due to its role in cellular respiration and energy production, making it an important tool for understanding how environmental pressures might be driving functional and morphological changes underpinned by genetic variation Species inhabiting the rapidly warming, yet diverse, biogeographic regions of South Africa and the Mediterranean Sea are likely locally adapted to their environment which can lead to differences in genetic variation among populations even in the face of high gene flow. Here, we sought to exploit the PacBio highly accurate long-amplicon sequencing technology to design a simple and cost-effective protocol to sequence a global collection of M. mustelus mitogenomes in parallel. This provided an opportunity to detect and independently assemble variants arising from heteroplasmy across the mitogenome. It also revealed hybridization amongst closely related houndshark species on the West Coast of South Africa. Comparison of mitogenomes from sampling populations collected across the species' global distribution range, revealed a high degree of divergence between geographical regions.

Keywords: genetic differentiation, PacBio sequencing, positive selection, heteroplasmy, hybridization, long range PCR